WEYDV-02-045

Nocturnal Raptor Monitoring Project - Slave Lake - 1999
Sponsor: 
Weyerhaeuser Company Limited
Lead Researcher: 
Roger Brown, Aspen Ecological Consulting, Edmonton, Alberta
Body: 
There are 13 species of owls recorded in Alberta, nine of which are known to breed in a forested habitat. All nine species of forest dwelling owls are thought to occur in the region defined by Weyerhaeuser’s Slave Lake Forest Management Agreement (FMA) area. The objectives of this project were to document the occurrence of owls in a wide range of forest types in the FMA, assess relative abundance and distribution of owls in different forest types, and establish permanent roadside survey routes that could be used in future years for the intent of monitoring owl populations.

Most forest-dwelling owl species can be surveyed effectively in the late winter and early spring using nighttime auditory surveys along roadsides. Nighttime surveys involved stopping at regularly spaced intervals (1.6km), broadcasting taped owl calls and listening for responding owls. Species that are active in the daytime are best surveyed by slowly driving along roadways with the driver and passenger searching from either side of the vehicle. The daylight surveys began two hours before dusk and were used to determine the presence of raptors active in the daytime (these species include hawks, eagles, falcons, accipiters, and some owl species especially Northern Hawk Owls, Northern Pygmy Owls, and Great Gray Owls). Eight permanent roadside survey routes were established within the FMA. Surveys began mid-February and finished at the end of April. All of the survey routes were sampled twice with the exception of one.

After adjusting for the double counting of owls, a total of 146 owls were identified at 107 stops. The only species that was not detected was the Short-eared owl, which usually breeds in tall grass prairie habitats, and tends to avoid continuously forest regions. The Northern Saw-whet Owl was the most frequently counted owl (54), with the Boreal Owl a close second (52). The Barred Owl was counted 22 times and the Great-horned Owl was counted 15 times. All other owls were rare, with the Great Gray Owl, Long-eared Owl, and the Northern Pygmy-Owl counted only once. To determine abundance and distribution of owls in different forest types the habitat within an 800-metre radius of each stop was characterized using AVI forest cover maps. There were no significant relationships identified between the habitat variables and owl species. The lack of relationship suggested that the sampling method was inadequate for the purposes of determining habitat preferences, and not an indication that habitat preferences do not exist. The sample sizes recommended to confirm population changes in most species in the FMA are significantly larger than what was sampled in 1999. Recommended changes to future owl survey methods are made in the full report.